Automatic current regulator



J an.

12, 1965 w. M. GRIMES, JR

AUTQMATIC CURRENT REGULATOR Filed June 20. 1961 FIG. I. 2 C l4 I I3 I 4 1 3 f l J HIGH VOLTAGE SUPPLY '9 FIXED VOLTAGE suPPLY7 1 MM I i I L l I ADJUSTABLE VOLTAGE suPPLY i 1 Y 4L 22o .A.C. A

SUPPLY FIG. 2.

VACUUM HIGH VOLTAGE PLATE SUPPLY 3 2 FIG. 3.

ADJUSTABLE emu -1 VOLTAGE SUPPLY W m 3 5 O 19 v-s v ADJUSTABl emu VOLTAGE SUPPLY J CURRENT I INVENTOR.

WILLARD M. GRIMES,Jr.

United States Patent ()1 Patented Jan. 12, 1965 3,165,571 AUTOMATIC CURRENT REGULATOR Willard M. Grimes, .lr., Wayne, N.J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pin, a cerporation of Pennsylvania Filed June 20, 1961, Ser. No. 118,389 5 Claims. (Cl. 13-1) This invention relates to electrical circuits and particularly to automatic self regulating circuits wherein compensation for a disturbance or deviation in one part thereof will be immediately and automatically provided within another part whereby the current flow in such a circuit may be maintained at a substantially even level.

The object of the invention is to provide rapidly operating and extremely sensitivemeans which will narrow the very minute range of the effects of operation of such an automatic circuit so that the'diiference between maximum current and minimum current implied by the expression substantially even will be narrowed still further.

Electrical regulator circuits in which means are employed in one part thereof to automatically compensate for any change in electrical characteristics in another part are conventional and all such circuits depend on a change to produce compensation. The present invention consti-' tutes an improvement in the art in that the value of the desired compensation is made responsive not merely to the value of the disturbance or deviation for which compensationmust be provided but to the rate at which the said disturbance or deviation-takes place.

The present invention may be disclosed, by way of example, as an automatic current regulator for an electron bombardment tungsten zone refining furnace where it is particularly necessary that the current flow be maintained at a substantially even level. The. means employed to produce compensation in the circuit to any disturbance or deviation in the current flow occurring in the furnace (including even a short circuit therein) is a non linear impedance element having a steeper slope in its current to voltagecharacteristic at the point fixed for the Operating value than the slope of the simple linear current to voltage characteristic would indicate. With such an element provided in the supply circuit of such a furnace any change in impedance within the furnace will tendto produce a change in the current flowing therethrough and such change in current will produce a change in impedance value of the said element whereby the current will be maintained at a substantially even'value. Since the said element has a; nonlinear characteristic the disturbance or deviation will produce an exaggerated or an plified efrect in the said impedance element with the result that the range of operation is materially narrowed,

that'is, the substantially even-currentvalue is more rigidly maintained. I t H Further, by way of example, a non linear impedance element may be provided in the form of tungsten filament lamps which are well known to have a steeply rising voltage current characteristic, that is a slope which is steeper than the slope of a simple linear-relationship at a'given point. Tungstenlamps have an advantage over ordinary resistors in that their incremental resistance re'=de/di is within their ordinary range of operation, always nearly twice the normal resistance Rr E/l. The gain of a feedback loop -isproportional to the incremental resistance, but the power lost in the current sensing resistor is proportional to the normal resistance. Hence the use of such -a non linear element as current sensing device in a feedback loop enables nearly twice as much current regulating precision to be obtained for a given power loss;

A feature of the invention is a feedback loop having a load circuit, such by way of example, as an electron bombardment refining furnace, energized by a source of current having means independent of the said loop and compensating means in the form of a current sensing means having non linear characteristics whereby the gain of such loop is proportional to the incremental resistance thereof whereas the power lost in said sensing means is proportional to the normal or steady state resistance thereof.

Another feature of the present invention is the use of an amplifier tube having a non linear cathode resistor whereby the incremental change produced by some deviation elsewhere in the circuit and sensed by the said cathode resistor is changed by the amplification factor of the tube.

In accordance with one form of the invention, the cathode resistor is made comparatively great by using a number of tungsten filament lamps in series so that the desired effect of amplifying the response of the feedback resistor to a change is made by amplifying (by the amplification factor of the tube) a comparatively great magnitude. In accordance with another form of the invention, the cathode resistor of the amplifier tube consists of a second amplifier tube and its cathode resistor consisting in this case of one or more tungsten filament lamps in parallel. Consequently the gain of the second tube and 7 its lesser magnitude cathode resistor is compounded by the firstv tube so that greater sensitivitymay thus be achieved. 1

Other features will appear hereinafter.

The drawings consist of a single sheet have three figures, as follows: 7 p f FIG. 1 is a schematic circuit diagram showing a feedback loop including a single amplifier tube and a series of tungsten lamps used as a current sensing device;

FIG. 2 is a schematic circuit diagram of an alternative arrangement using a plurality of tungsten lamps in mul-' tipleand a plurality of tubes in the current path; and

FIG. 3 is agraph showing the characteristic current voltage relationship of a non linear resistor such as a tungsten lamp and the normal linear culrent voltage characteristic passing through the same desired fixed value at which the device is operated.

In the following description, certain'values and certain specific types of apparatus are set forth as an aid tungsten zone refining furnace 1 to a preset value. The

electron tube Vl in FIG. 1 and the tubes V2 and V3 in FIG. 2, which are controlled by means independent of the feedback loop, are employed to maintain a steady loop current while providing a high difference of potential across the elements of the electrode bombardment furnace and acting as amplifiers of the reaction of the current sensing resistor. i The current path may be traced from the highvoltage plate supply 2, over the conductor 3, through the secondary of the transformer 4, the bombardment electrode 5, the tungsten rod 6 (slowly moved through theelement 5) the resistance unit consisting of a series of tungsten filaamplifier tube V1, conductor 8 to the other terminal of transformer 7, the cathode and the anode of the power amplifier tube VI, conductor 8 to the other terminal'of the power supply element 2.3 The current flow in this loop is adjusted by the potential applied tothe grid of the tube V1 here shown as coming from a fixed voltage amplification factor of the tube V3. p I

mental resistance of the paralleled lamps 15, 16 and 17 3 supply 9 in combination with an adjustable voltage supply 10 interconnected in any convenient and conventional manner. The voltage of the unit 10 may be regulated by the use of an autotransformer 11 whereby the power supplyto the transformer 12 may be changed by manual adjustment of the device 11. In like manner the output of the high voltage supply may be regulated by the use of an adjustable autotransforrner 13 whereby the power supply to the transformer 14 may be changed by manual adjustment of the device 13.

In accordance with. the present invention, the current in the loop is limited by a feedback resistor shown here as a series of lamps R11 to R115 inclusive. Any disturbance in the circuit, such by way of example, as a random increase in bombardment current, will tend to increase the voltage drop across this feedback resistance with the result that the said increase in current will be almost equalled and nullified. An important feature of the present invention is that the feedback resistance consists of tungsten filament lamps whereby the non linear resistance characteristics of this element greatly increases the sensitivity thereof and operates to narrow the margin in the variation in current value. Thus, substantially constant current may be maintained in'the loop even during the occurrence ofshort circuits in the furnace while it is operating at high voltage, say. by Way of example, at 3000 volts across the bombardment gap. Under such extreme conditions, the regulators still control the current so that itdoes not exceed more than a few percent of'the current flowing when such 3000 volt furnace is operating normally. a In the feedback circuit described, the feedback element consists of tungsten filament lamps which have an advantage over ordinary resistors in that their incremental resistance re=de/di is always, in the zone of normal operation, nearly twice the normal resistance R=E/lf. It may be noted in FIG. 3 that the tungsten lamp voltage current characteristic 20 is very much steeper, say at the point R, than the normalvolta'ge current characteristic 21 passing through this same point. In FIG. 2, where the. furnace 1 and transformer 4 of FIG. 1 may be fitted'at the line A-A (the 220 V. AC. supply-being assumed to be connected to the high voltage tungsten filament lamps 15, 16 and 17 connected in paralplate supply, the voltage supply 18, the voltage supply 19 Y and the transformer 4 in like manner to that shown in. FIG. 1) the feedback resistance consists of one. or more lel and there are two power amplifier tubes V2 and V3 connected in series each of whose grids are controlled by a separate adjustable voltage supply 18 and 19 respectively. The advantage of the use of more than one electron tube in the feedback circuit will be pointed out hereinafter.

FIG. 2 shows 'a circuit in which the high incremental resistance of the current sensing lamp is multiplied bythe If re is the increand M is the increase in voltage across the lamps due I to an'increase in current, Ai, then A'e is equal to the product 'reAi. The increase in voltage across tube V3 is equal to the productreAi multiplied by ,u, the amplification factor of the tube. on tube V2 is equal to the sum of, the increment Ae and A63 (the incremental'voltage increase across the tube V3); f Since Ae equals real, and Ae;; equals ,aAe which equals ,uJeAi', then Ae eFAe =re(p-{-,1)Ai.

The cathode voltage increase sum of the Voltage across the lamps (15, 16 and 17) plus the voltage across V3. This change in voltage, as shown above, is equal to' re(,u+l.)Ai. This voltage change is multiplied by the amplification factor of V2 which may 'be'also equal to the amplification factor of V3. The total voltage change across theseries circuit V2, V3 and the lamps is equal to the sum Ae +e +Ae The voltage Ae is equal to re (n+1)Ai The voltage change Ac +e has already been shown to be re(,u+1)Ai. Thus the total voltage change Ae developed by a small change in current, Ai,'lS re( t[-1)Ai+re( .+1)Ai t. For a one ampere regulator, a typical value of re is 165 ohms and a typical value-of a is 50. .Substituting in Ae re(,a]l)Ai+re( .t+1)Ai i gives 165 51Ai+165 51 50Ai which substantially reduces to 8,400Ai+420,000hi. Thus 428,400Az' is the total increment of voltage Ae that would be developed against an incremental increase incurrent Ai.

Ae ;428,400Ai. 1

If a furnace operating at 3000 volts shorts out, a change of voltage, Ae of 3000 volts is impressed upon'the remainder of the circuit, which is the series string V2, V3 and the lamps 15, 16 and 17.

ae izaooogai aoomzsooogm 1122.007 ampere of controlling a three kilowatt furnace from a five kilowatt power supply so that even a short circuit in the it furnace cannot drive the current to within 4 percent above normal.

across the series string of lamps R11 to R115 is reAi.

This increment of voltage-is multiplied-by the amplification factor, t, of the tube V1. The incremental voltage reAi is added to the voltage reAi developed across the tube. A. The voltage increment across the series of lamps, and the voltage increment across the tube V1, add up. to a total incremental increase in voltage of Y re(;t ,-1)Ai. In a one ampere regulator using a FIG- URE 1 circuit configuration re is 165 ohms per lamp and g 15 lamps given a dynamic resistance of '15. times 165 I which equals 2480 ohms. However, the normal resist- I ance is only 1340ohms which at ,a current of one ampere dissipates 1340 watts in addition to thevl000 watts dissipated by the tube V1. Again, assuming. an amplification factor ofr50, the total incremental change for an incremental current change Ai, is (15) (165) (50+,1)z .i, which yields 126,000Ai which is a little lessthan'l/(a ofthe gain that would be realized using anothertubeinstead of the 15 lamps. The ,additionaltube of the FIGLZ circuit consumes a kilowatt in platediSsipation, but this tube has a regulating effectiveness of n+1 or 51- lamps which would require (5 1) (1) (89 2volts) or 4550 Watts, over 4.5 6 times that dissipatedthe I tube;

' power for operating only 26. The FIG. 2 circuit is even more spectacular'in this .;Since the grid 'of V2 is fiXed, the input signal to Vzis i the cathode voltage. The cathode voltage of V2 is the It is to be noted from this comparison of the FIG. 1' circuit and the FIG. 2. circuit that each stage multiplies;

the dynamic'resistance of the lamps; by n+1. FIGjl is the equivalent of (.51) -(15) .or 765 ballast lamps in g, series with the furnace. 'Yet the FIG. 1 circuitconsumes i ,in normal plate dissipation (1 5) (89 2) +l000 watts for a total of 2340watts. This would be consumed i only 26 lamps so that it appears that the FIG. c rcuit gives the ballasting-etfect of 765 lamps but respect. "(51) which is equivalent to 2601 ballast lamps, yet con- Hence requires the l It-has the regulating'eff'ectiveness of ('1) ('51)- sumes in normal plate dissipation the equivalent power of only 23 lamps.

As a detailed specific example for practicing the present invention, the electrical circuit as shown in FIG. 1 will be considered and all voltages will be given with respect to the outputterminal of the furnace 1, which is grounded. The tube ,V1 is a type 5669. The potential applied to the anode of the tube V1 is 2340 volts above ground. The potential applied to the grid of tube V1 is 1460 volts above ground. The cathode of the tube V1 normally has applied thereto a potential of 1340 volts above ground. The non-linear resistor is formed of fifteen 150 watt, 125 volt conventional incandescent lamps, connected in series. Accordingly, the normal potential drop which occurs across these series-connected lamps is 1340 volts. The potential applied at the input terminal or cathode 5 of the electron beam Zone refining furnace 1 is 3000 volts below ground. Any decrease in electrical resistance in the furnace 1 will increase the potential drop across the non-linear resistor. This in turn will be reflected as an increase in potential above ground as applied at the cathode of the tube V1 to limit the current drawn by the tube V1 and stabilize the current through the circuit. The normal current through the entire circuit is approximately 1 ampere. seen that when an overload occurs, the cathode potential is moved in a positive fashion with respect to the predetermined potential which is applied to the grid of the tube V1 in order to control the current. It should be understood that the foregoing specific example has only been given by way of illustration and is subject to considerable modification.

While in acordance with the patent statutes, one best example has been illustrated and described in detail, it is to be particularly understood that the invention is not limited thereto or thereby.

I claim:

1. An electron-beam, zone-refining furnace and the electric power source therefor, said furnace comprising a cathode connected to a furnace electrical input terminal and an anode comprising the object being refined and connected to a furnace electrical output terminal, said furnace normally operating with a predetermined current passing therethrough, said electric power source comprising:

(a) electron power tube means having an anode, a cathode, and a control grid, said tube means during operation of said furnace acting to pass the operating current drawn by said furnace;

(b) first DC. potential source means having an output potential of predetermined value and connected across the input terminals of said furnace and the anode of said tube means; I

(0) second DC. potential source means adapted to apply to the grid of said tube means a potential of predetermined value; and

(d) non-linear feedback impedance means connected in series between said tube means and said furnace, and said non-linear impedance means during normal operation of said furnace having a predetermined voltage drop thereacross and displaying a resistance which increases with increasing voltage drop thereacross.

2. An electron-beam, zone-refining furnace and the electric power source therefor, said furnace comprising a cathode connected to a furnace electrical input terminal and an anode comprising the object'being refined and connected to a furnace electrical output terminal, said furnace normally operating with a predetermined current passing therethrough, said electric power source com- It will be (b) first DC. potential source meanshaving an output potential of predetermined value and connected across the input terminals of said furnace and the anode of said tube means;

(0) second DC. potential source means adapted to apply to the grid of said tube means a potential of predetermined value; and

(d) non-linear impedance means connected between the output terminal of said furnace and the cathode of said tube means, and said non-linear impedance means during normal operation of said furnace having a predetermined voltage drop thereacross and displaying a curve of voltage drop thereacross versus current therethrough which has a slope considerably greater than the slope of a similar curve taken for a linear resistor.

3. The combination as specified in claim 2, wherein said non-linear impedance comprises tungsten filamentary wire.

4. An electron-beam, zone-refining furnace and the electric power source therefor, said furnace comprising a cathode connected to a furnace electrical input terminal and an anode comprising the object being refined and connected to a furnace electrical output terminal, said furnace normally operating with a predetermined current passing therethrough, said electric power source comprising:

(a) a plurality of electron power tube means each having an anode, a cathode, and a control grid, said tube means during operation of said furnace acting to pass the operating current drawn by said furnace, and the anode of the first of said tube means connected to the cathode of the vnext-succeeding of said tube means;

(1)) first DC. potential source means having an output potential of predetermined value and connected across the input terminals of said furnace and the anode of the last of said tube means;

(c) second DC. potential source means adapted to apply to the grid of each of said tube means electric potential of predetermined value; and

(d) non-linear impedance means connected between the output terminal of said furnace and the cathode of the first of said tube means, and said non-linear impedance means during normal operation of said furnace having a predetermined voltage drop thereacross and displaying a curve of voltage drop there across versus current therethrough which has a slope considerably greater than the slope of a similar curve taken for a linear resistor.

5. An electron-beam, zone-refining furnace and the electric power source therefor, said furnace comprising a cathode connected to a furnace electrical input terminal and an anode comprising the object being refined and connected to a furnace electrical output terminal, said furnace normally operating with a predetermined current passing therethrough, said electric power source comprising:

(a) first electron power tube means having an anode,

a cathode, and a control grid;

([2) power amplifier electron tube means having an anode, a cathode, and a control grid, the anode of said first tube means connected to the cathode of said amplifier tube means;

(c) first DC. potential source means having an output potential of predetermined value and connected across the input terminals of said furnace and the anode of said amplifier tube means; 7 I

(0!) other DC. potential source means adapted to apply bias excitation to the grids of all said tube means; and

(e) non-linear impedance means connected between the output terminal of said furnace and the cathode of said first tube means, and said non-linear impedance means during normal operation of said furnace having a predetermined voltage drop there- 7 across and displaying a curve of voltage drop thereacross versus current therethrough which has a slope considerably greater than the slope of a similar curve taken for a linear resistor.

References Cited in the file of this patent UNITED STATES PATENTS 1 ,252,502 Shreeve Jan. 8, 1918 Ziegler Nov; 1 6, 1928 Griggs June-9, 1931 Claesson Dec. 29, 1942 4 FOREIGN PATENTS l Great Britain June 16, 1927 Great Britain July 11, 1928 Canada 1 Mar. 23, 1954' 

1. AN ELECTRON-BEAM, ZONE-REFINING FURNACE AND THE ELECTRIC POWER SOURCE THEREFOR, SAID FURNACE COMPRISING A CATHODE CONNECTOR TO A FURNACE ELECTRICAL INPUT TERMINAL AND AN ANODE COMPRISING THE OBJECT BEING REFINED AND CONNECTED TO A FURNACE ELECTRICAL OUTPUT TERMINAL SAID FURNACE NORMALLY OPERATING WITH A PREDETERMINED CURRENT PASSING THERETHROUGH, SAID ELECTRICAL POWER SOURCE COMPRISING: (A) ELECTRON POWER TUBE MEANS HAVING AN ANODE, A CATHODE, AND A CONTROL GRID, SAID TUBE MEANS DURING OPERATION OF SAID FURNACE ACTING TO PASS THE OPERATING CURRENT DRAWN BY SAID FURNACE; (B) FIRST D.C. POTENTIAL SOURCE MEANS HAVING AN OUTPUT POTENTIAL OF PREDETERMINED VALUE AND CONNECTED ACROSS THE INPUT TERMINALS OF SAID FURNACE AND THE ANODE OF SAID TUBE MEANS; (C) SECOND D.C. POTENTIAL SOURCE MEANS ADAPTED TO APPLY TO THE GRID OF SAID TUBE MEANS A POTENTIAL OF PREDETERMINED VALUE; AND (D) NON-LINEAR FEEDBACK IMPEDANCE MEANS CONNECTED IN SERIES BETWEEN SAID TUBE MEANS AND SAID FURACE, AND SAID NON-LINEAR IMPEDANCE MEANS DURING NORMAL OPERATION OF SAID FURNACE HAVING A PREDETERMINED VOLTAGE DROP THEREACROSS AND DISPLAYING A RESISTANCE WHICH INCREASES WITH INCREASING VOLTAGE DROP THEREACROSS. 